The present invention generally relates to a method for writing a magnetic head positioning signal into a magnetic disk, and also to an apparatus capable of writing a magnetic head positioning signal to a magnetic disk. More specifically, the present invention is directed to a method for writing a magnetic head positioning signal, to a writing apparatus thereof, and to a positioning-signal write head, and furthermore to a magnetic disk apparatus (HDA) containing a magnetic disk manufactured by the above-described method, which are suitable for canceling a positioning error caused by an unequal thickness of a magnetic film of a magnetic disk, and also by an unbalanced distribution of magnetic powder contained in the magnetic film.
A conventional apparatus for writing a magnetic head positioning signal employed in a conventional magnetic disk apparatus utilizes a laser length measuring machine or the like as a position detector and also utilizes a positioning control system in which a voice coil motor (hereinafter referred to as a "VCM") is used as a drive source. Thus, a positioning-signal write/ read head is positioned to a predetermined position on a radius of the magnetic disk, and then the positioning signals are then sequentially written on the respective tracks of the magnetic disk in a unit of one track from an outer diameter side thereof As a consequence, the positioning errors are contained in the positioning signal, which are synchronized with rotations of the magnetic disk and caused by an unequal (uneven) thickness of a magnetic film due to a surface shape of a magnetic disk substrate, and by an unequal distribution of magnetic powder contained in the magnetic film.
A description will now be made of the above-described positioning error contained in the positioning signal in more detail FIG. 1 represents a magnetic disk plane for writing a positioning signal. The positioning signal is over-written into write tracks W(n-1), W(n), W(n+1), W(n+2) and so on by the positioning-signal write unit 4g (see FIG. 6) of the head slider part of the magnetic head. Subsequently, the positioning-signal read unit 4f of the head slider part of the magnetic head is sequentially positioned onto read tracks R(n-2), R(n-1), R(n), R(n+1) and R(n+2), whereby the positioning signals written on the magnetic disk in a coaxial form are sequentially read out. It should be noted, as shown in FIG. 1, that the write tracks W(n-1), W(n), W(n+1) and W(n+2) are positionally and mutually shifted with respect to the read tracks R(n-2), R(n-1), R(n), R(n+1) and R(n+2) by 1/2 track pitch
As a result, assuming now that the positioning-signal read unit 4f is positioned to the read track Rn, this positioning-signal read unit 4f reads out the positioning signals which have been written on both of the write track Wn and the write track W(n+1), a position signal proportional to a difference in the signals output from both of these write tracks, is formed by a demodulator (not shown), and then a plurality of magnetic heads (not shown) are positioned to predetermined tracks in response to this position signal
FIG. 2 is a sectional view of the magnetic disk plane shown in FIG. 1, taken along a line II--II illustrated in FIG. 1. As represented in the drawing, the positioning-signal read unit 4f is floated on the write tracks Wn and W(n+1) (on the read track R(n)) this is. Since the positioning signals written into the write tracks W(n) and W(n+1) are brought into a saturation writing state, the outputs thereof are directly proportional to both a thickness of a magnetic film at the write tracks W(n) and W(n+1) under the positioning-signal read unit 4f, and the amount of magnetic powder contained in the magnetic film. It should be noted that the thickness of the magnetic film 2d is varied in accordance with surface machining precision of the magnetic disk substrate 2c, whereas the amount of magnetic powder (indicated by a dot in FIG. 2) is changed, depending upon the unequal distribution.
Referring now to FIG. 3, a description will be made of adverse influences caused by the unequal thickness of the magnetic film and also the unequal distribution of the magnetic powder, and also given to the positioning signals It should be noted that FIG. 3 only represents the vibration components of the position signals in synchronism with the rotation of the magnetic disk. In FIG. 3, an ordinate is indicated by a value which is obtained by converting the vibration component of the position signal into the positioning error amount, whereas an abscissa is indicated by a rotation angle of the magnetic disk It should be understood that the position signal shown in FIG. 3 corresponds to the output of the position signal when the positioning-signal read unit 4 is positioned over the read track R(n) shown in FIG. 1, and the vibrations of the position signal corresponding to the head travel distance of about 3 .mu.m happen to occur, due to the unequal thickness of the magnetic film and the unequal distribution of the magnetic powder contained therein Since the vibrations of the position signal are caused by the unequal thickness of the magnetic film of the magnetic disk and also the unequal distribution of the magnetic powder contained therein, the vibrations are synchronized with the rotation of the magnetic disk.
With respect to such vibrations of the position signal caused by the uneven distribution of the magnetic powder contained in the magnetic film, the conventional writing apparatus employs the following measurement. That is to say, after the positioning signals have been written into the entire plane of the magnetic disk, the positioning signals are read out by the read head and demodulated to obtain position signals Then, amplitudes of the vibrations of the position signals are measured, and also the track pitches are measured If the measurement results exceed the specification values, the positioning signals are rewritten in the same manner, or the present magnetic disk is replaced by a new magnetic disk for rewriting the positioning signals thereto Also, various improvements have been performed in the surface machining precision of the magnetic disk substrate so that the thickness of the magnetic film could be uniformly made and the distribution of the magnetic powder contained in the magnetic film could be equally made, whereby the vibrations of the position signals could be improved
Heretofore, the positioning errors which are caused by the unequal distribution of the magnetic powder contained in the magnetic film and also are synchronized with the rotation of the magnetic disk, are smaller than the track pitch for recording the data Also the adverse influences by these positioning errors and given to the positioning precision on the data write/read (R/W) head, are relatively low. However, there is a problem in the adjustments or corrections of the positioning errors which are synchronized with the rotation of the magnetic disk, since the track pitches become narrower due to high data recording density.
The above-described conventional positioning-signal write method and apparatus are known from, for example, JP-A-64-48276, which describes a measurement for preventing the vibrations of the magnetic disk caused by the mechanical rotation vibrations of the rotating mechanism for rotating the magnetic disk.
As previously described in the prior art, no care is taken into the positioning errors which are caused by the unequal thickness of the magnetic film of the magnetic disk substrate and the unequal distribution of the magnetic powder contained in the magnetic film and also are synchronized with the rotation of the magnetic disk As a consequence, when the data recording track pitches are narrowed in accordance with an increased recording capacity of the magnetic disk recording apparatus, the above-described positioning errors synchronized with the magnetic disk may cause a large adverse influence to the positioning precision of the data write/read head, and therefore may impede the high data recording density.
Moreover, the above-explained conventional improvements in achieving the uniform thickness of the magnetic film and also the uniform distribution of the magnetic powder contained in the magnetic film, due to the surface machining precision of the magnetic disk substrate, will induce a high cost. Additionally, since there is a limitation in the surface machining precision of the magnetic disk substrate, such a conventional surface machining precision does not improve the positioning precision required for the high data recording density.